The present invention relates to modified polyolefin compositions having improved mechanical strength.
It has been heretofore known that the mechanical, chemical, electrical, and thermal properties of polyolefin resins can be improved by admixing fillers such as wood powder, chaff, and calcium carbonate into the resins. However, because of their hydrophilic property, this type of fillers has low compatibility with the polyolefin resins which are hydrophobic. Therefore, mere blending and kneading of the two kinds of materials cannot provide satisfactory composite products. Various attempts have been made to improve the "compatibility" between such fillers and the polymer matrix. One method comprises coating the surface of the fillers with various materials or reacting such materials with the fillers to promote the "compatibility." Another method includes kneading surface active agents into the polymer matrix. In addition, the use of polymers having a polar group as the polymer matrix has been practiced.
However, these methods require a coating process, a special reaction process, or the addition of a large quantity of a surface active agent, thereby resulting in increasing the complexity of the processes and higher cost.
We have studied the compatibility between these fillers and the polyolefins by means of an electron microscope and have found that even with the introduction of polar groups into the polymer matrix, ample penetration of the matrix into the micro voids of the fillers cannot be attained.
On the basis of this knowledge, we have made various attempts to make the fillers and the polymer matrix compatible with each other. As a result, we found that when a radical generating agent and wood powder are added to a polyolefin composed primarily of propylene, and the mixture is kneaded at an increased temperature, the polyolefin penetrates well into the micro voids (passageways) of the wood powder, thereby improving the properties of the polyolefin.
Additionally, we found that when the radical generating agent is used in conjunction with an appropriate amount of a polar vinyl monomer, the penetration of the polyolefin into the micro voids of the wood powder is promoted, whereby the physical properties of the polyolefin composite are further improved together with the polarization of the matrix.
Similar results can be obtained with the use of other porous fillers such as finely divided chaff, zeolite, and the like instead of the wood powder.